Imaging device

ABSTRACT

An imaging device including: a semiconductor substrate having a first surface and a second surface opposite to the first surface; a microlens located closer to the first surface than to the second surface; and a first photoelectric converter located between the first surface and the microlens. The first photoelectric converter includes a first electrode, a second electrode, and a photoelectric conversion layer that is located between the first electrode and the second electrode and that converts light into electric charges. The first photoelectric converter is the closest of any photoelectric converter existing between the first surface and the microlens to the first surface. The imaging device includes no photodiode as a photoelectric converter, and a focal point of the microlens is located below a lowermost surface of the photoelectric conversion layer.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.17/077,013, filed on Oct. 22, 2020, which is a Continuation of U.S.patent application Ser. No. 16/145,008, filed on Sep. 27, 2018, now U.S.Pat. No. 10,847,555, which claims the benefit of Japanese ApplicationNo. 2017-200556, filed on Oct. 16, 2017, the entire disclosures of whichapplications are incorporated by reference herein.

BACKGROUND 1. Technical Field

The present disclosure relates to stacked type imaging devices.

2. Description of the Related Art

Solid state imaging devices are widely used for digital still cameras,digital video cameras, and the like. Known examples of the image sensorinclude MOS such as complementary metal oxide semiconductor (CMOS) imagesensors, and charge coupled device (CCD) image sensors. In recent years,CMOS image sensors, having low power supply voltage, are widely used assolid state imaging devices mounted on mobile devices such ascamera-equipped cell phones and smartphones in view of powerconsumption. Japanese Unexamined Patent Application Publication No.H05-48980 discloses an imaging device having microlenses.

SUMMARY

Imaging devices having high sensitivity to incident light and high lightresistance are desired.

One non-limiting and exemplary embodiment provides the following device.

In one general aspect, the techniques disclosed here feature an imagingdevice including: a semiconductor substrate having a first surface and asecond surface opposite to the first surface; a microlens located closerto the first surface than to the second surface; and a firstphotoelectric converter located between the first surface and themicrolens. The first photoelectric converter includes a first electrode,a second electrode, and a photoelectric conversion layer that is locatedbetween the first electrode and the second electrode and that convertslight into electric charges. The first photoelectric converter is theclosest of any photoelectric converter existing between the firstsurface and the microlens to the first surface, the imaging devicecomprises no photodiode as a photoelectric converter, and a focal pointof the microlens is located below a lowermost surface of thephotoelectric conversion layer.

A general or specific aspect may be embodied by an element, device,module, system, integrated circuit, or method. Further, a general orspecific aspect may be embodied by any combination of an element,device, module, system, integrated circuit, and method.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an imaging device according to areference example;

FIG. 2 is a schematic sectional view of an imaging device according toan embodiment;

FIG. 3A and FIG. 3B are views which illustrate a height of a microlensand a gap between microlenses adjacent to each other in a diagonaldirection, respectively;

FIG. 4 is a view which shows the results of optical simulation;

FIG. 5 is a graph that represents the relationship between the height ofthe microlens and a normalized degree of light concentration, and therelationship between the height of the microlens and the normalizedquantum efficiency reduction rate;

FIG. 6 is a view which illustrates a degree of light concentration in afirst region;

FIG. 7 is a graph that illustrates the result of simulation on therelationship between the height of the microlens and a normalizedquantum efficiency;

FIG. 8 is a graph that illustrates the result of simulation on therelationship between the height of the microlens and a normalizedeffective incident angle;

FIG. 9 is a graph that represents the relationship between a distancefrom an uppermost surface of a semiconductor substrate to a focal pointand the normalized degree of light concentration, and the relationshipbetween the distance from the uppermost surface of the semiconductorsubstrate to the focal point and the normalized quantum efficiencyreduction rate;

FIG. 10 is a graph that illustrates the result of simulation on therelationship between the distance from the uppermost surface of thesemiconductor substrate to the focal point and the normalized quantumefficiency;

FIG. 11 is a graph that illustrates the result of simulation on therelationship between the distance from the uppermost surface of thesemiconductor substrate to the focal point and the normalized effectiveincident angle;

FIG. 12 is a schematic sectional view of an imaging device according toa modified example of an embodiment; and

FIG. 13 is a schematic sectional view of an imaging device according toanother modified example of an embodiment.

DETAILED DESCRIPTION Underlying Knowledge Forming Basis of the PresentDisclosure

In image sensors, light sensitivity is of importance. In order toimprove light sensitivity, microlenses are typically used. FIG. 1 is aschematic sectional view of an image sensor 101 according to a referenceexample on which microlenses are mounted. In the image sensor 101, alight-shielding layer 104 is formed in an insulating interlayer 105 soas to prevent light incident on a region 103, which is a region otherthan a light-receiving element 102. On the insulating interlayer 105, acolor filter layer 106, which includes color filters 106 a, 106 b, and106 c, is disposed. On the color filter layer 106, a protectiveinsulating film 107 having a planarized upper surface is disposed inorder to improve planarization or light transmittance. On the protectiveinsulating film 107, microlenses 108 for converging light are disposed.

Typically, the light-receiving element 102 is, for example, photogate orphotodiode. The light-shielding layer 104 is made of a material such asmetal. The microlens 108 is made of a material such as polymeric resin.The protective insulating film 107 is made of a material such as asilicon oxide based thin film, and typically has the same refractiveindex as that of the microlens. The microlens 108 is typically convex onone surface and planarized on the other surface. In the image sensor 101of the reference example, the microlens 108 is convex on the uppersurface, and planarized on the lower surface that is in contact with theprotective insulating film 107. That is, the microlens 108 of thereference example is a convex lens having a convex shape only on theupper surface. Further, in the image sensor 101 of the referenceexample, the microlens 108 and the protective insulating film 107 haveapproximately the same refractive index. Moreover, in the image sensor101 of the reference example, the convex lens is designed to have afocal distance which is the same as the distance from the convex lens tothe light-receiving element. Accordingly, incident light can beefficiently focused on the light-receiving element 102. JapaneseUnexamined Patent Application Publication No. H05-48980 discloses animaging device in which the microlens is designed to have a focaldistance which is equal to or less than a distance between the microlensand the photodiode.

However, in the case of stacked type imaging device which uses anorganic thin film as a light-receiving element, it is not alwayssuitable to have the focal distance of the microlens which issubstantially equal to the distance between the microlens and thelight-receiving element.

For example, when strong light such as sunlight is incident on themicrolens and focused to be incident on the light-receiving element, thelight-receiving element may be damaged. Specifically, image quality ofthe imaging device may be decreased due to a decrease in lightsensitivity or burn-in.

The present disclosure has been made in light of the above issue oflight resistance, and it is desired to provide an imaging device havinghigh light resistance as well as light sensitivity by designing anappropriate shape for the microlens.

An aspect of the present disclosure is summarized below.

[Item 1]

An Imaging Device Including:

a semiconductor substrate having a first surface;

a microlens located above the first surface of the semiconductorsubstrate; and

one or more photoelectric converters located between the first surfaceof the semiconductor substrate and the microlens, each of the one ormore photoelectric converters including a first electrode, a secondelectrode located closer to the microlens than the first electrode is,and a photoelectric conversion layer that is located between the firstelectrode and the second electrode and that converts light into electriccharges, wherein a focal point of the microlens is located below alowermost surface of the photoelectric conversion layer of a firstphotoelectric converter, the first photoelectric converter being locatedclosest to the first surface of the semiconductor substrate among theone or more photoelectric converters.

[Item 2]

The imaging device according to the item 1, wherein the focal point ofthe microlens is located between the lowermost surface of thephotoelectric conversion layer of the first photoelectric converter andthe first surface of the semiconductor substrate.

[Item 3]

The imaging device according to the item 1 or 2, further including awiring layer located between the first surface of the semiconductorsubstrate and the photoelectric conversion layer of the firstphotoelectric converter, wherein the focal point of the microlens isoverlapped with the wiring layer in a plan view.

[Item 4]

The imaging device according to any one of the items 1 to 3, furtherincluding a color filter located between the microlens and the one ormore photoelectric converters.

[Item 5]

The imaging device according to any one of the items 1 to 4, wherein theone or more photoelectric converters include a second photoelectricconverter located between the first photoelectric converter and themicrolens.

[Item 6]

The imaging device according to any one of the items 1 to 4, wherein thephotoelectric conversion layer includes an organic material.

Further, an aspect of the present disclosure is summarized below.

An imaging device according to an aspect of the present disclosure is animaging device including a semiconductor substrate, and a plurality ofpixels disposed on the semiconductor substrate, wherein each of theplurality of pixels includes an upper electrode that transmits light, alower electrode located below the upper electrode, a photoelectricconverter located between the upper electrode and the lower electrodeand converting light into electric charge, a microlens located above thephotoelectric converter, and a signal detecting section that outputs asignal corresponding to the electric charge, and, when a distance fromthe vertex of the microlens to the uppermost surface of thephotoelectric conversion layer is defined as X and a distance from thevertex of the microlens to the focal point is defined as Y, the Y islarger than the X.

Thus, since the distance Y from the vertex of the microlens to the focalpoint and the distance X from the vertex of the microlens to theuppermost surface of the photoelectric conversion layer satisfy therelationship of Y>X, the incident light converged by the microlens andentering the photoelectric conversion layer with the highest lightintensity can be reduced. Accordingly, optical damage, such as burn-in,to the photoelectric conversion layer can be reduced to thereby improvelight resistance of the imaging device. Further, reduction in quantumefficiency can be suppressed.

For example, in the imaging device according to an aspect of the presentdisclosure, the focal point of the microlens may be located below thelowermost surface of the photoelectric conversion layer, and may belocated above the uppermost surface of the semiconductor substrate.

With this configuration, the light with high light intensity is reducedor prevented from being converged on the uppermost surface of thephotoelectric conversion layer to thereby reduce optical damage to thephotoelectric conversion layer. Accordingly, light resistance of theimaging device can be improved, and reduction in quantum efficiency canbe suppressed. Further, since the photoelectric conversion layer canreceive incident light at a large area and perform photoelectricconversion, the photoelectric conversion efficiency can be improved.Further, since the incident light becomes less likely to reach thesemiconductor substrate, occurrence of photoelectric conversion in thesemiconductor substrate can be reduced. Accordingly, unnecessaryelectric charge becomes less likely to occur in the semiconductorsubstrate, and thus the noise can be reduced.

For example, in the imaging device according to an aspect of the presentdisclosure, a wiring layer may be disposed at a position of the focalpoint of the microlens.

With this configuration, incident light is scattered by the wiringlayer, which causes the incident light to be less likely to reach thesemiconductor substrate. Accordingly, occurrence of photoelectricconversion in the semiconductor substrate can be reduced.

With reference to the drawings, an embodiment of the present disclosurewill be described in detail.

The embodiment described below includes a general or specific example.Numerical values, shapes, components, arrangement positions andconnection forms of the components, steps, the order of steps, and thelike specified in the embodiment described below are merely an example,and are not intended to limit the present disclosure. Among thecomponents in the embodiment described below, components that are notrecited in independent claims which show the highest concept aredescribed as optional components. The drawings are not necessarily toscale. Throughout the drawings, configurations which are substantiallythe same are denoted by the same reference signs, and the duplicateddescription thereof may be omitted or simplified.

Embodiment

FIG. 2 is a sectional view of an imaging device 200 according to thepresent embodiment.

The imaging device 200 according to the present embodiment is an imagingdevice which includes a semiconductor substrate 210, and a plurality ofpixels 211 disposed over the semiconductor substrate 210. The pluralityof pixels 211 each include a photoelectric converter 212, a microlens208, and a signal detecting section 209. The photoelectric converter 212includes an upper electrode 204 that transmits light, a lower electrode202 located below the upper electrode 204, and a photoelectricconversion layer 203 located between the upper electrode 204 and thelower electrode 202 and converting light into electric charges. Themicrolens 208 is located above the photoelectric converter 212. Thesignal detecting section 209 outputs a signal corresponding to theelectric charge obtained by the photoelectric converter 212.

Further, the imaging device 200 includes an insulating film 205 disposedon the upper electrode 204 of the photoelectric converter 212, a colorfilter layer 206 disposed on the insulating film 205, and a planarizingfilm 207 disposed on the color filter layer 206. The color filter layer206 includes green color filters 206 a, blue color filters 206 b, andred color filters 206 c. The color filters of the respective colors arearranged corresponding to the pixels 211 and according to Bayer pattern.

Further, the imaging device 200 includes an insulating interlayer 201located below the photoelectric conversion layer 203, and asemiconductor substrate 210 located below the insulating interlayer 201.The semiconductor substrate 210 is provided with an electric chargeaccumulation region for accumulating electric charges, and a signaldetecting section 209. The signal detecting section 209 is formed, forexample, by combining a plurality of transistors such as CMOStransistors. For example, the signal detecting section 209 includes anamplifying transistor that outputs a signal corresponding to theelectric charge accumulated in the electric charge accumulation region,and a reset transistor that resets the electric charge accumulationregion. The gate of the amplifying transistor is connected to theelectric charge accumulation region. The source or drain of the resettransistor is connected to the electric charge accumulation region. Theelectric charge accumulation region is connected to the lower electrode202.

Further, the photoelectric conversion layer 203 may be made of aninorganic material or an organic material. The inorganic material maybe, for example, amorphous silicon. When an organic material is used, ann-type organic semiconductor and a p-type organic semiconductor materialmay be joined.

In the following description, an example in which the photoelectricconversion layer 203 is made of an organic material will be described.

As illustrated in FIG. 2 , a distance from the vertex of the microlens208 to the uppermost surface of the photoelectric conversion layer 203is defined as X, and a distance from the vertex of the microlens 208 tothe focal point of the microlens is defined as Y. In the imaging device200 according to the present embodiment, Y is larger than X. Since thedistance Y from the vertex of the microlens to the focal point of themicrolens is different from the distance X from the vertex of themicrolens to the uppermost surface of the photoelectric conversionlayer, the incident light converged by the microlens and entering thephotoelectric conversion layer with the highest light intensity can besuppressed. Moreover, when Y>X is satisfied, light can be prevented frombeing converged at the center of pixels. Accordingly, optical damage,such as burn-in, to the photoelectric conversion layer can be suppressedto thereby improve light resistance of the imaging device. Further,reduction in quantum efficiency can be suppressed.

In the imaging device 200 according to the present embodiment, theposition of the focal point of the microlens 208 may be located belowthe lowermost surface of the photoelectric conversion layer 203, or maybe located above the uppermost surface of the semiconductor substrate210. That is, the position of the focal point of the microlens 208 maybe located between the lowermost surface of the photoelectric conversionlayer 203 and the uppermost surface of the semiconductor substrate 210.Accordingly, the light with high light intensity converged inside thephotoelectric conversion layer 203 can be suppressed or prevented tothereby suppress optical damage to the photoelectric conversion layer203. In addition, the light resistance of the imaging device 200 can beimproved, and thus reduction in the quantum efficiency can besuppressed. Further, since the photoelectric conversion layer 203 canreceive incident light at a large area and perform photoelectricconversion, the photoelectric conversion efficiency can be improved.Further, since the incident light becomes less likely to reach thesemiconductor substrate 210, occurrence of photoelectric conversion inthe semiconductor substrate 210 can be suppressed. Accordingly,unnecessary electric charge is less likely to occur in the semiconductorsubstrate 210, and thus the noise can be suppressed.

In the imaging device 200 according to the present embodiment, a wiringlayer may be disposed at a position of the focal point of the microlens208. When a wiring layer is positioned in the insulating interlayer 201,incident light is scattered by the wiring layer, which causes theincident light to be less likely to reach the semiconductor substrate.Accordingly, occurrence of photoelectric conversion in the semiconductorsubstrate 210 can be reduced. The focal point of the microlens 208 maybe overlapped with the wiring layer in plan view. In this configurationas well, the incident light becomes less likely to reach thesemiconductor substrate 210.

In general, a focal distance f of the microlens 208 is represented bythe following formula (1):

f={n1/(n1−n0)}R  (1)

In the formula (1), R is a radius of curvature of the microlens 208, n1is a refractive index of a material of the microlens 208, and n0 is arefractive index of a medium that is in contact with the light-incidentside of the microlens 208.

That is, the formula (1) represents the focal distance f of themicrolens 208 when light is incident on the microlens 208 having therefractive index n1 and the radius of curvature R, from a medium (forexample, an air layer) having the refractive index n0.

When the height of the microlens 208 is h and the radius of the bottomof the microlens 208 is r, the radius of curvature R of the microlens208 is represented by the following formula (2):

R=(r ² +h ²)/2h  (2)

FIGS. 3A and 3B are views which illustrate a height h of the microlens208 and a gap L between the microlenses 208 adjacent to each other inthe diagonal direction. FIG. 3A is a schematic sectional view of thepixel 211. In the figure, a configuration below the color filter layer206 is not illustrated. FIG. 3B is a plan view of four pixels 211.

As illustrated in FIG. 3A, the height h of the microlens 208 is a lengthfrom the bottom of the microlens 208 to the vertex of the microlens 208.Further, as illustrated in FIG. 3B, the gap L between the microlenses208 adjacent to each other in the diagonal direction is a distancebetween the bottoms of two microlenses 208 adjacent to each other in thedirection of a diagonal line of a pixel unit, which is composed of fourpixels 211. A radius r of the bottom of the microlens 208 is determineddepending on the size of the pixel 211 and the gap L.

In the following description, an optical simulation is described whichis performed with the height h of the microlens 208 being varied in theimaging device 200. The imaging device 200 includes the pixels 211 eachhaving a square shape with a side length of 3.0 μm, and the microlensesthe gap L of which is 800 nm between the microlenses 208 adjacent toeach other in the direction of a diagonal line. Specifically, a waveoptical simulation based on Babinet's principle is used. In everysimulation described herein, the bottom of the microlens 208 has acircular shape in plan view, and the radius r of the bottom of themicrolens 208 is calculated based on the size of the pixel 211 being 3.0μm and the gap L between the microlenses 208 being 800 nm.

First, the above formulas (1) and (2) are used to obtain the focaldistance f with respect to the height h of the microlens 208. Thedistance Y from the vertex of the microlens 208 to the focal point iscalculated by adding a distance from the principal point to the vertexof the microlens to the focal distance f. In the formula (1), n0 is arefractive index of air (n0=1.0), and n1 is a refractive index of themicrolens 208 (n1=1.6). The result of the simulation is shown in Table1.

Table 1 shows the relationship, which depends on the height of themicrolens 208, between the distance Y from the vertex of the microlens208 to the focal point and the distance X from the vertex of themicrolens 208 to the uppermost surface of the photoelectric conversionlayer 203. The X is a value in the case where a distance from theuppermost surface of the photoelectric conversion layer 203 to theuppermost surface of the planarizing film 207 is 1590 nm.

TABLE 1 Height h (nm) 200 400 600 800 1000 1200 1400 1600 Distance 125126506 4615 3753 3302 3058 2930 2877 Y (nm) to focal point Distance 17901990 2190 2390 2590 2790 2990 3190 X (nm) to photo- electric conversionlayer

With reference to Table 1, when the side length of the pixel 211, thegap L of the microlenses 208 in the direction of diagonal line, and theheight h of the microlens 208 are set as described above, the higher theheight h of the microlens 208, the smaller the focal distance f of themicrolens 208. That is, the higher the height h of the microlens 208,the smaller the distance Y from the vertex of the microlens 208 to thefocal point. On the other hand, the higher the height h of the microlens208, the larger the distance X from the vertex of the microlens 208 tothe uppermost surface of the photoelectric conversion layer.

In the simulation, the focal point of the microlens 208 is alsocalculated. In the simulation, the thickness of the photoelectricconversion layer 203 is assumed as 500 nm, the thickness of theinsulating interlayer 201 (that is, a distance from the lowermostsurface of the photoelectric conversion layer 203 to the uppermostsurface of the semiconductor substrate 210) is assumed as 3500 nm, andthe thickness of the semiconductor substrate 210 is assumed as 775 nm.Here, the focal point of the microlens 208 at every height of themicrolens 208 shown in Table 1 is as described below.

When the height of the microlens 208 is 200 nm, the focal point of themicrolens 208 is located below the semiconductor substrate 210. When theheight of the microlens 208 is 400 nm, the focal point of the microlens208 is located in the semiconductor substrate 210. When the height ofthe microlens 208 is 600 nm, 800 nm, and 1000 nm, the focal point of themicrolens 208 is located in the insulating interlayer 201. When theheight of the microlens 208 is 1200 nm, the focal point of the microlens208 is located in the photoelectric conversion layer 203. When theheight of the microlens 208 is 1400 nm, the focal point of the microlens208 is located in the insulating film 205 on the upper electrode 204.When the height of the microlens 208 is 1600 nm, the focal point of themicrolens 208 is located above the upper electrode 204.

Specifically, a distance Z (nm) from the uppermost surface of thesemiconductor substrate 210 to the focal point of the microlens 208 isrepresented as X+4000−Y (nm) when a direction from the semiconductorsubstrate 210 toward the microlens 208 is assumed as a positivedirection. Accordingly, the relationship between the height h of themicrolens 208 and the distance Z from the uppermost surface of thesemiconductor substrate 210 to the focal point is as shown in Table 2.Here, the distance Z of 0 (nm) corresponds to the uppermost surface ofthe semiconductor substrate 210. The distance Z of 3500 (nm) correspondsto the lowermost surface of the photoelectric conversion layer 203. Thedistance Z of 4000 (nm) corresponds to the uppermost surface of thephotoelectric conversion layer 203. Accordingly, when the height h ofthe microlens 208 is 200 nm and 400 nm, the focal point is located belowthe uppermost surface of the semiconductor substrate 210. When theheight h of the microlens 208 is 600 nm, 800 nm, and 1000 nm, the focalpoint is located between the uppermost surface of the semiconductorsubstrate 210 and the lowermost surface of the photoelectric conversionlayer 203. When the height h of the microlens 208 is 1200 nm, the focalpoint is located in the photoelectric conversion layer 203. When theheight h of the microlens 208 is 1400 nm and 1600 nm, the focal point islocated above the uppermost surface of the photoelectric conversionlayer 203.

TABLE 2 Height h (nm) 200 400 600 800 1000 1200 1400 1600 Distance 125126506 4615 3753 3302 3058 2930 2877 Y (nm) to focal point Distance 17901990 2190 2390 2590 2790 2990 3190 X (nm) to photo- electric conversionlayer Distance −6722 −516 1575 2637 3288 3732 4060 4313 Z (nm) fromsemi- conductor substrate surface to focal point

Next, a simulation on a light converging state is performed. In thesimulation, the pixel has a square shape with a side length of 3.0 μm,and a gap L is 800 nm between the microlenses adjacent to each other inthe direction of a diagonal line. Light is radiated onto the imagingdevice having these microlenses to check a light converging state on theuppermost surface of the photoelectric conversion layer, which dependson the height h of the microlens. The light used for the simulation hasa wavelength of 530 nm. Hereinafter, a “square cell having a side lengthof x μm” is referred to as an “x μm cell”.

FIG. 4 is a view which shows the results of optical simulation for theimaging device having a 3.0 μm cell. FIG. 4(a) is a schematic diagram ofa pixel region (hereinafter, also referred to as an observation region)where a light converging state is observed. FIGS. 4(b) to 4(j) are viewswhich show light intensity on the uppermost surface of the photoelectricconversion layer. In these views, a black part represents low lightintensity, and a white part represents high light intensity.

As illustrated in FIG. 4(a), green color filters (G), blue color filters(B), and red color filters (R) are arranged corresponding to therespective pixels and according to Bayer pattern, and the observationregion includes the green pixel and part of the peripheral pixels.

FIGS. 4(b), 4(c), 4(d), 4(e), 4(f), 4(g), 4(h), 4(i), and 4(j) show thelight converging state when the height h of the microlens is 0 nm (i.e.,without microlens), 200 nm, 400 nm, 600 nm, 800 nm, 1000 nm, 1200 nm,1400 nm, and 1600 nm, respectively.

As shown in FIGS. 4(b) to 4(j), the higher the height h of themicrolens, the smaller the distance Y from the vertex of the microlensto the focal point. Light incident on the microlens is graduallyconverged to a point at the center of pixel in plan view.

Specifically, the lower the height h of the microlens, the larger thedistance Y from the vertex of the microlens to the focal point(hereinafter, simply referred to as “the distance Y to the focalpoint”). When the distance Y to the focal point becomes larger than thedistance X from the vertex of the microlens to the uppermost surface ofthe photoelectric conversion layer (hereinafter, simply referred to as“the distance X to the photoelectric conversion layer”), the focal pointof the microlens moves to a position below the uppermost surface of thephotoelectric conversion layer. Accordingly, a degree of lightconcentration on the uppermost surface of the photoelectric conversionlayer decreases. The degree of light concentration refers to anintegrated value of light intensity per unit area in the center part ofpixel in plan view.

On the other hand, when the height h of the microlens increases, thedistance Y to the focal point decreases and becomes closer to thedistance X to the photoelectric conversion layer. That is, as the heighth of the microlens increases, the focal point of the microlens becomescloser to the uppermost surface of the photoelectric conversion layerand thus the degree of light concentration on the uppermost surface ofthe photoelectric conversion layer increases.

Next, a simulation is performed on the relationship between the height hof the microlens and the degree of light concentration on the uppermostsurface of the photoelectric conversion layer. The result is describedbelow. Further, an image sensor is prototyped with the height h of themicrolens being varied to evaluate the relationship between the height hof the microlens and the reduction in quantum efficiency. The result isdescribed below.

In the following description, as illustrated in FIG. 6 , a “firstregion” refers to a region in the center part of the 3.0 μm cell, andthe region has a square shape with a side length of 1.0 μm. The degreeof light concentration in the first region refers to an integrated valueof light intensity in the first region. A “normalized degree of lightconcentration” refers to a normalized value of degree of lightconcentration in the first region for each height h of the microlens onthe assumption that the degree of light concentration in the firstregion is 1 when a microlens is not provided, that is, when the height hof the microlens is 0 nm. The “quantum efficiency” refers to a ratio ofthe amount of light absorbed by the photoelectric conversion layer tothe amount of incident light. The “quantum efficiency reduction rate”refers to a difference between the quantum efficiency before lightradiation and the quantum efficiency after radiation of light at 100,000lux for 150 hours. The “normalized quantum efficiency reduction rate”refers to a normalized value of quantum efficiency reduction rate foreach height h of the microlens on the assumption that the quantumefficiency reduction rate is 1 when the height h of the microlens is1400 nm.

FIG. 5 is a graph that represents the relationship between the height hof the microlens and the normalized degree of light concentration in thefirst region, and the relationship between the height h of the microlensand the normalized quantum efficiency reduction rate. In FIG. 5 , thesolid line represents the result of the normalized degree of lightconcentration for each height h of the microlens obtained from asimulation. The dotted line represents the result of the normalizedquantum efficiency reduction rate obtained from an experiment.

As seen from the graph indicated by the solid line in FIG. 5 , light ismore likely to be converged at the center of pixel in plan view with anincrease in the height h of the microlens. In particular, it is foundthat an increase rate in the normalized degree of light concentration islarge when the height h of the microlens is in the range fromapproximately 600 nm to approximately 1200 nm. Further, as seen from thegraph indicated by the dotted line in FIG. 5 , the quantum efficiency ismore likely to decrease after light radiation with an increase in theheight h of the microlens. Accordingly, it seems that, since light ismore likely to be converged at the center of pixel in plan view with anincrease in the height h of the microlens, deterioration of thephotoelectric conversion layer is more likely to occur at around thecenter of the pixel, leading to a decrease in quantum efficiency.

In other words, as the distance Y from the vertex of the microlens tothe focal point becomes larger than the distance X from the vertex ofthe microlens to the uppermost surface of the photoelectric conversionlayer, the degree of light concentration at the center of pixel in planview decreases. Accordingly, the quantum efficiency is less likely todecrease after light radiation.

Therefore, when the relationship Y>X is satisfied, light can beprevented from being converged at the center of pixels, and thus thephotoelectric conversion layer can be prevented from receiving opticaldamage such as burn-in. Accordingly, light resistance of the imagingdevice can be improved, and reduction in quantum efficiency can besuppressed.

Then, a simulation is performed on the relationship between the height hof the microlens and the quantum efficiency. In the simulation, animaging device having a configuration illustrated in FIG. 2 is used.FIG. 7 is a graph that represents the result of simulation performed onthe relationship between the height h of the microlens and thenormalized quantum efficiency.

The “normalized quantum efficiency” refers to a normalized value ofquantum efficiency for each height h of the microlens on the assumptionthat the quantum efficiency is 1 when a microlens is not provided, thatis, when the height h of the microlens is 0 nm.

As illustrated in the graph in FIG. 7 , in the imaging device having aconfiguration illustrated in FIG. 2 , the quantum efficiency becomesmaximum when the height h of the microlens is in the range fromapproximately 600 nm to approximately 800 nm.

Subsequently, a simulation is performed on the relationship between theheight h of the microlens and the light converging characteristics ofthe microlens. In this simulation as well, an imaging device having thesame configuration as that in the simulation of normalized quantumefficiency is used. FIG. 8 is a diagram that represents the result ofsimulation performed on the relationship between the height h of themicrolens and the normalized effective incident angle.

The “effective incident angle” refers to an incident angle of light whenthe quantum efficiency is 0.8 on the assumption that the quantumefficiency of the light incident on a G (green) pixel at 0° (that is,vertically) is 1 when light having a wavelength of 530 nm is radiatedonto the G pixel corresponding to the green color filter. The“normalized effective incident angle” refers to a normalized value ofeffective incident angle for each height h of the microlens on theassumption that the effective incident angle is 1 when the height h ofthe microlens is 0 nm. The graph in FIG. 8 illustrates that, as thenormalized effective incident angle increases, light in wider range ofincident angle can be converged by the microlens and used forphotoelectric conversion.

As seen from the graph in FIG. 8 , in the imaging device having aconfiguration illustrated in FIG. 2 , the effective incident angle ishigh when the height h of the microlens is in the range fromapproximately 800 nm to approximately 1200 nm. In particular, it isfound that the effective incident angle is maximum when the height ofthe microlens is approximately 1000 nm.

From the results of simulation as described above, when the height h ofthe microlens is 1400 nm, the relationship between the distance Y to thefocal point and the distance X to the photoelectric conversion layer isY≈X (Y<X), and the focal point of the microlens is located slightlyabove the uppermost surface of the photoelectric conversion layer, thatis, located in the upper electrode. Here, as seen from FIG. 4(i) and thegraph indicated by the solid line in FIG. 5 , the light intensity on theuppermost surface of the photoelectric conversion layer is high, and thedegree of light concentration is also high. However, as indicated by thedotted line in FIG. 5 , the quantum efficiency reduction after lightradiation is the highest when the height h of the microlens is 1400 nm.

When the height h of the microlens is 1000 nm, 800 nm, and 600 nm, Y>Xis satisfied. When the height h of the microlens is 1000 nm, the focalpoint of the microlens is located in the lower electrode. Further, whenthe height h of the microlens is 800 nm and 600 nm, the focal point ofthe microlens is located in the insulating interlayer. In addition, awiring layer is disposed in the insulating interlayer. As indicated bythe dotted line in FIG. 5 , when the relationship between the distance Yto the focal point and the distance X to the photoelectric conversionlayer satisfies Y>X, and the focal point of the microlens is locatedbelow the uppermost surface of the photoelectric conversion layer andabove the uppermost surface of the semiconductor substrate,deterioration after light radiation can be suppressed. Further, asillustrated in FIGS. 7 and 8 , when the height h of the microlens is inthe range from 600 nm to 1200 nm, the quantum efficiency and theeffective incident angle are improved.

According to the present disclosure, in the stacked type solid stateimaging device, light converging efficiency and light resistance can beimproved by setting the focal point of the microlens at a position belowthe uppermost surface of the photoelectric conversion layer. Further,light converging efficiency and light resistance can be improved bysetting the focal point of the microlens at a position below thelowermost surface of the photoelectric conversion layer and above thesemiconductor substrate. The microlens of the present disclosure can beimplemented, for example, by modifying a coating thickness and a lightexposure amount in production of microlens by using a conventionalprocess and material.

As described above, since the imaging device of the present disclosurecan mitigate the degree of light concentration to the photoelectricconversion layer without reducing quantum efficiency, optical damage tothe photoelectric conversion layer can be reduced.

As described above, the relationship between the height h of themicrolens and the distance Z from the uppermost surface of thesemiconductor substrate to the focal point of the microlens is shown inTable 2. Accordingly, the graphs illustrated in FIGS. 5, 7, and 8 canalso be represented with a horizontal axis representing the distance Zfrom the uppermost surface of the semiconductor substrate to the focalpoint. Here, the description will be made based on the graph having thehorizontal axis representing the distance Z.

FIG. 9 , which corresponds to FIG. 5 , represents the relationshipbetween the distance Z from the uppermost surface of the semiconductorsubstrate to the focal point and the normalized degree of lightconcentration, and the relationship between the distance Z from theuppermost surface of the semiconductor substrate to the focal point andthe normalized quantum efficiency reduction rate. FIG. 10 , whichcorresponds to FIG. 7 , represents the relationship between the distanceZ from the uppermost surface of the semiconductor substrate to the focalpoint and the normalized quantum efficiency. FIG. 11 , which correspondsto FIG. 8 , represents the relationship between the distance Z from theuppermost surface of the semiconductor substrate to the focal point andthe normalized effective incident angle. In the respective drawings, Thedistance Z of 0 (nm) corresponds to the uppermost surface of thesemiconductor substrate 210. The distance Z of 3500 (nm) corresponds tothe lowermost surface of the photoelectric conversion layer 203. Thedistance Z of 4000 (nm) corresponds to the uppermost surface of thephotoelectric conversion layer 203.

As illustrated in FIG. 9 , when the focal point is located below thelowermost surface of the photoelectric conversion layer (i.e., Z<3500),the normalized degree of light concentration decreases and thus thenormalized quantum efficiency reduction rate decreases. That is,durability can be improved by setting the focal point to be locatedbelow the lowermost surface of the photoelectric conversion layer.Further, as illustrated in FIG. 10 , when the focal point is locatedbelow the lowermost surface of the photoelectric conversion layer (i.e.,Z<3500), the normalized quantum efficiency is high. Thus, durability aswell as sensitivity can be improved by setting the focal point to belocated below the lowermost surface of the photoelectric conversionlayer. Further, as illustrated in FIG. 11 , when the focal point islocated below the lowermost surface of the photoelectric conversionlayer (i.e., Z<3500), the normalized effective incident angle is large.That is, light in a wider range of incident angle can be converged andused for photoelectric conversion by setting the focal point to belocated below the lowermost surface of the photoelectric conversionlayer.

The imaging device according to the present disclosure has beendescribed with reference to the embodiment. However, the presentdisclosure is not limited to the above embodiment. It should be notedthat, without deviating from the spirit of the present disclosure,another embodiment formed by applying various modification conceived bya person having ordinary skill in the art to the above embodiment, or bycombining part of components of the above embodiment is also included inthe scope of the present disclosure. A modified example of the presentembodiment will be described below.

The imaging device 200 illustrated in FIG. 2 includes the color filterlayer 206 between the photoelectric converter 212 and the microlens 208.However, the color filter layer 206 may not be necessarily provided.FIG. 12 is a schematic sectional view of an imaging device according toa modified example. An imaging device 300 illustrated in FIG. 12 isdifferent from the imaging device 200 illustrated in FIG. 2 in that theplanarizing film 207 is formed directly on the insulating film 205. Inthe configuration of the imaging device 300 illustrated in FIG. 12 aswell, the focal point of the microlens 208 may be set to be locatedbetween the uppermost surface of the semiconductor substrate 210 and thelowermost surface of the photoelectric conversion layer 203. With thisconfiguration, the same effect as that described for the imaging device200 illustrated in FIG. 2 can be obtained.

Further, the imaging device 200 illustrated in FIG. 2 includes only onephotoelectric converter 212 between the semiconductor substrate 210 andthe microlens 208. However, a plurality of photoelectric converters maybe provided between the semiconductor substrate 210 and the microlens208. FIG. 13 is a schematic sectional view of an imaging deviceaccording to another modified example. An imaging device 400 illustratedin FIG. 13 is different from the imaging device 200 illustrated in FIG.2 in that an insulating film 405 and a photoelectric converter 412 areprovided between the photoelectric converter 212 and the insulating film205. In the imaging device 400 illustrated in FIG. 13 , the focal pointof the microlens 208 may be set to be located between the uppermostsurface of the semiconductor substrate 210 and the lowermost surface ofthe photoelectric conversion layer 203 and between the uppermost surfaceof the semiconductor substrate 210 and the lowermost surface of thephotoelectric conversion layer 403. That is, the focal point of themicrolens 208 may be set to be located between the uppermost surface ofthe semiconductor substrate 210 and the lowermost surface of thephotoelectric conversion layer 203 which is closest to the semiconductorsubstrate 210. With this configuration, the same effect as thatdescribed for the imaging device 200 illustrated in FIG. 2 can beobtained for each of the photoelectric conversion layer 203 and thephotoelectric conversion layer 403. In addition, in the configurationhaving layers of three or more photoelectric converters, the same effectcan be obtained by employing the similar configuration.

The imaging device of the present disclosure can be applied to camerassuch as digital cameras and vehicle-mounted cameras.

What is claimed is:
 1. An imaging device comprising: a semiconductorsubstrate having a first surface and a second surface opposite to thefirst surface; a microlens located closer to the first surface than tothe second surface; and a first photoelectric converter located betweenthe first surface and the microlens, the first photoelectric converterincluding a first electrode, a second electrode, and a photoelectricconversion layer that is located between the first electrode and thesecond electrode and that converts light into electric charges, whereinthe first photoelectric converter is the closest of any photoelectricconverter existing between the first surface and the microlens to thefirst surface, the imaging device comprises no photodiode as aphotoelectric converter, and a focal point of the microlens is locatedbelow a lowermost surface of the photoelectric conversion layer.
 2. Theimaging device according to claim 1, further comprising a wiring layerlocated between the first surface of the semiconductor substrate and thephotoelectric conversion layer of the first photoelectric converter,wherein the focal point of the microlens is overlapped with the wiringlayer in a plan view.
 3. The imaging device according to claim 1,further comprising a color filter located between the microlens and thefirst photoelectric converter.
 4. The imaging device according to claim1, further comprising a second photoelectric converter located betweenthe first photoelectric converter and the microlens.
 5. The imagingdevice according to claim 1, wherein the photoelectric conversion layerincludes an organic material.
 6. The imaging device according to claim1, further comprising a signal detecting circuit that detects theelectric charges from the first photoelectric converter, wherein thefirst electrode is located between the photoelectric conversion layerand the semiconductor substrate, the focal point of the microlensoverlaps with the first electrode in a plan view, the focal point of themicrolens is located above the signal detecting circuit.
 7. The imagingdevice according to claim 6, wherein the focal point of the microlens islocated above the first surface of the semiconductor substrate.
 8. Animaging device comprising: a semiconductor substrate having a firstsurface and a second surface opposite to the first surface; a microlenslocated closer to the first surface than to the second surface; and atleast one photoelectric converter located between the first surface andthe microlens, each of the at least one photoelectric converterincluding a first electrode, a second electrode, and a photoelectricconversion layer that is located between the first electrode and thesecond electrode and that converts light into electric charges, whereinthe at least one photoelectric converter includes a first photoelectricconverter that is the closest of any photoelectric converter existingbetween the first surface and the microlens to the first surface, theimaging device comprises only the at least one photoelectric converteras a photoelectric converter, and a focal point of the microlens islocated below a lowermost surface of the photoelectric conversion layer.9. The imaging device according to claim 8, further comprising a wiringlayer located between the first surface of the semiconductor substrateand the photoelectric conversion layer of the first photoelectricconverter, wherein the focal point of the microlens is overlapped withthe wiring layer in a plan view.
 10. The imaging device according toclaim 8, further comprising a color filter located between the microlensand the first photoelectric converter.
 11. The imaging device accordingto claim 8, further comprising a second photoelectric converter locatedbetween the first photoelectric converter and the microlens.
 12. Theimaging device according to claim 8, wherein the photoelectricconversion layer includes an organic material.
 13. The imaging deviceaccording to claim 8, further comprising a signal detecting circuit thatdetects the electric charges from the first photoelectric converter,wherein the first electrode is located between the photoelectricconversion layer and the semiconductor substrate, the focal point of themicrolens overlaps with the first electrode in a plan view, the focalpoint of the microlens is located above the signal detecting circuit.14. The imaging device according to claim 13, wherein the focal point ofthe microlens is located above the first surface of the semiconductorsubstrate.